There is a natural difference between the energy levels of microwave transmissions from fixed station cell transmitters and from cellular phone transmitters. Fixed station cell transmitters have significantly higher power and considerably larger and better antennas than possible with cellular phone transmitters.
Fixed cell sites operate over the 870-890 MegaHertz (MHz) band (called the "forward" channels) while cellular phone units operate over the 825-845 MHz band (called the "reverse" channels).
A result of the large differences in energy levels of the respective signals from fixed station cell transmitters and cellular phone transmitters is that in many situations a receiver which is monitoring such transmissions can easily receive cellular base station radio frequency (RF) signals (herein called "forward channel RF signals" or "forward channel signals" or similar wording) but cannot receive adequate energy levels of radio frequency signals from cellular phone transmitters (herein called "reverse channel RF signals" or "reverse channel signals" or similar wording).